1. Field of the Invention
The present invention relates to document feeding apparatus in general and, more particularly, the invention relates to a combined recirculating automatic document feeder (RADF) and a semiautomatic document feeder (SADF).
2. Prior Art
The use of document feeders for advancing sequential pages of a document onto the exposure platen of an electrophotographic copier for copying, is well known in the prior art. Prior art document feeders can be broadly classified into three groups; namely, automatic document feeders (ADF), recirculating document feeders (RADF) and semiautomatic document feeders (SADF).
U.S. Pat. No. Re 27,976 (Sahley) is an example of prior art ADF. The ADF is adapted to feed the pages of a document to be copied from a document supply station to the copying or viewing window of a copier duplicator. Once a page is correctly positioned on the document platen, the imaging mechanism of the copier is initiated and a latent image of the page is formed on the photoconductor of the copier. The image is subsequently processed to form a copy of the original page.
The ADF of the subject patent consists of a document supply station and a document receiving station. The document supply station and the document receiving station are disposed on opposite sides of the viewing window and in linear alignment therewith. Each of the stations includes a document support tray and a sheet feed mechanism for feeding a sheet from the bottom of the tray. Each of the document support trays is fitted with a slot through which a page enters or leaves the tray. At the supply station, the sheet leaves the tray through the slot. At the receiving station, the sheet enters the tray through the slot. A movable gate is disposed relative to each slot and guides an extracted sheet onto the exposure platen.
In operation, an operator loads a stack of sheets to be copied into one of the trays. The sheets are arranged so that the side of the page containing the printed matter faces downwardly with page one being at the bottom of the stack. If multiple or collated sets of the document are needed, the operator sets the feeder accordingly to indicate the number of sets. The feed mechanism feeds the first sheet of the document from the bottom of the stack onto the exposure platen. After copying, the document is returned to the other receiving tray which is disposed on the opposite side of the platen. The process continues until all the pages of the document are copied and are stacked at the receiving tray. If the feeder had been set to provide multiple copies of the document, the document would then be fed page-by-page from the receiving tray onto the viewing window there it would be exposed and stacked into the supply tray. The process continues until the document is exposed the desired number of times to the copying machine to provide a selected number of copies. When the document has been fed the required number of times, the feeder is automatically shut off.
Although the ADF works satisfactorily for its intended purpose, it tends to be costly. Additionally, the use of a document supply and document receiving station unduly expands the overall length of the copier to which they are attached. As described above, the ADF is comprised of two identical sections. Each section includes identical parts and as such, increase the overall cost. Similarly, the length of the system increases because the section must be attached to opposite sides of the document exposure platen.
In addition to the above defects, the Sahley patent lacks the capability of processing a duplex original so that both sides of the document can be copied at the document platen.
In an attempt to solve the defects associated with the above-described patent, the prior art introduced the recirculating automatic document feeder. This type of document feeder is disposed above the document platen or exposure platen of the copier. The feeder includes a single document supply tray which is positioned above the platen. Documents to be copied are placed on the tray. Pages of the documents are transported in sequence to the platen where they are exposed and then returned to the stack. If multiple sets of a document are selected, each page of the document will be exposed for a predetermined number of times at the exposure platen.
U.S. Pat. No. 4,176,945 (Holzhauser et al.) is an example of the prior art recirculating feeder. This recirculating feeder also includes a document positioner. The recirculating feeder consists of a hopper which is placed above the exposure platen and in spaced relation thereto. The bottom of the hopper is fitted with an opening through which pages of original documents are sequentially extracted. A reciprocating vacuum device is disposed relative to the opening. The document positioner consists of a sheet feed device disposed along a paper path separate and distinct from the nonrecirculating paper path.
In operation, a multipage document is placed in the hopper. The document is placed with the pages arranged in normal sequential order. The first page is at the top of the stack and the last page at the bottom. The printed information is also arranged in normal sequential order with side one of each page facing upwardly. As sheets are extracted from the bottom of the stack, they are forced to traverse a first curved channel path. As a result, the sheet is turned over with the side one facing downwardly in the platen. A plurality of feed rollers are disposed on the platen and position the sheet for copying. If the sheet is a simplex copy, it is forced to traverse a second curve channel where it is inverted and is fed onto the top of the stack with side one facing upwardly.
If the sheet has printing on both sides (duplex original), after it is picked from the stack it is transported across the platen and it is forced to follow a third curve channel path where it is flipped and side two is placed on the document platen for copying. After copying, the sheet is forced to follow the third curve channel where it is again flipped and is positioned on the document glass for side one copying. After side one is copied, the document is transported along the second curve channel where it is flipped and is restacked on top of the stack with side one facing upwardly. A sheet diverter is disposed at the junction of the second and third curve channel paths and divert the sheet to follow the appropriate path.
The recirculating feeder is also fitted with a document positioner. The document positioner handles odd-sized sheets which cannot be accommodated by the recirculating section of the feeder or normal-sized sheets when only a few copies are needed. The document positioner consists of a tray on which document sheets are placed with information to be copied facing downwardly. The sheet is advanced manually from the tray until the leading edge of the sheet activates a switch whereupon a plurality of feed rollers feed the sheet into a registration mechanism. From the registration mechanism, the sheet is fed onto the copier platen. After copying, the sheet is fed through the third curved path to an output tray. It should be noted that for duplex originals, the throughput of the above recirculating feeder is reduced. The reduction in throughput partly occurs because for duplex originals, the sheet is transported across the document platen to the duplex inverting sheet path. The inverted sheet is then brought back to the platen where side two is copied. The sheet is transported for a second time through the duplex inverting path and is brought back to the platen for side one copying. The sheet is then forced to follow the recirculating path where it is flipped and is placed in the sheet support bin with side one facing upwardly.
It should be noted that the first time that a duplex original is transported over the platen, the sheet is not copied and as such, valuable time is wasted which results in reduction in the throughput. Any attempt to copy the sheet in the first pass will result in the sheets being placed in the reverse order in the document tray. If the original sheets are in reverse order (that is side two of each page facing upwardly) one cannot make multiple sets of a multipage document with the copy sheets for each set arranged in sequential order.
U.S. Pat. No. 4,099,150 (Connin) is another example of prior art devices which circulate and recirculate original documents for copying. The device is capable of presenting simplex and duplex originals for copying. The device consists of a pair of document holding hoppers disposed in spaced relationship on top of one another in a vertical orientation. Duplex documents to be copied are placed in the upper hopper with the odd side of each page facing upwardly. The documents are fed from the top of the upper hopper inverted, and placed in the lower hopper. The documents are then fed from the bottom of the lower hopper onto the platen so that the even side of each document is copied. After copying, the document is inverted and is placed on the top of the stack in the second hopper. The bottom feed procedure is repeated and the odd side of each page is copied. The pages are then stacked into the upper hopper.
U.S. Pat. No. 4,140,387 is yet another example of a prior art recirculating document feeder. The recirculating feeder consists of a receiving hopper in which a set of sheets to be copied is placed with the printed information facing upwardly. The sheets are prepared for copying by inverting them and placing them in a second hopper. The sheets are then transported through a plurality of complex arcuate paths to the document platen of a copier for simplex (one-sided) or duplex (two-sided) copying.
U.S. Pat. No. 4,169,674 is still another prior art recirculating document feeder which circulates sheets for simplex copying at the platen of a convenience copier. The recirculating document feeder consists of a document supply tray disposed above the platen of the convenience copier. A single loop paper path interconnects the exit end of the tray to the input end. A pair of rotating vacuum cylinders are disposed, one at each end of the tray. As a sheet is extracted from the tray, it is flipped by one of the cylinders. As it is restacked in the tray, the sheet is again flipped by the other cylinder. Although the paper path is relatively simple, the device cannot handle duplex originals.
Although the above-described document feeders work well for their intended purposes, the paper path along which a document is transported tends to be complex. This complexity tends to reduce the throughput of documents handled by the devices. The degradation in throughput is particularly pronounced when duplex originals are being handled.
Another type of problem which is associated with complex paper paths is that the document feeders are susceptible to paper jams and ultimate damage to original documents.
Another general type of problem which is associated with the above-described prior art document feeders is their inability to reposition a previously copied sheet on the document glass (without recycling through the sheets in the stack) for recopying. Oftentimes a paper jam or other malfunction occurs in a copier machine. As a result, a transfer image is destroyed with the copy sheet. In order to form a complete set of copy sheets, it is necessary to replace the original sheet for reexposure, etc. However, due to the fact that the prior art document handlers make a direct transfer of original sheets from the exposure platen to the sheet supply tray, they cannot perform consecutive exposure of a previously exposed sheet. Of course, by recycling through the stack to the point where the sheet is placed, one may be able to obtain and reposition the sheet for reexposure. However, such a procedure is time-consuming, complex and is therefore unacceptable.